For lead, nickel-metal hydride, or lithium-ion batteries, monitoring of the deterioration of the battery and thereby ultimately of the battery life is of great importance for functional endurance. Generally, the deterioration or battery life corresponds to the so-called “cycle life”, which indicates the possible number of charge and discharge cycles of a battery before it stops functioning. Besides the absolute number of cycles, the type of the respective cycles, and here in particular the depth to which the battery is discharged or recharged, are of importance for this cycle life. Thus, for example, given a depth of discharge 100% per cycle, a battery has a cycle life of 80 cycles on a statistical average; however, given a depth of discharge 1% per cycle, it has a cycle life of 30,000 cycles. That is, for each depth of charge/discharge, there exists a number of cycles which is equivalent to the battery life. The total battery life is reached, for example, after 200,000 cycles at a depth of discharge (DOD) of 0.75%, or after 20,000 cycles at a DOD of 2.5%, etc.
Of the three battery systems mentioned at the outset, the lead battery has the shortest cycle life and the lowest cost of acquisition. Therefore, here is the greatest need for suitable monitoring or prognosis of the remaining cycle life.
Based on this knowledge, German Patent Application DE 198 49 163 A1 proposes an integrated storage device in batteries and accumulators, allowing storage and evaluation of data that is interesting for the service life of the batteries. Unfortunately, the above-mentioned document does not allow any conclusions about the actual mode of operation and especially not on the evaluation of the stored data so that no teaching is provided here that could be used by one skilled in the art to implement a method for determining the deterioration of a battery.
U.S. Pat. No. 5,739,670 proposes a method for diagnosing the condition of batteries. Using suitable counters, charge cycles and charge quantities as well as the duration of charge and discharge processes are measured and counted. The values determined in this manner are modified by an e-function via a correspondingly complex relationship in such a manner that the general condition of the battery can be calculated therefrom.
The procedure is comparatively complex, because a corresponding amount of data must be acquired and mathematically combined in complex form to be able to make the comparatively vague statements on the general condition of the battery.
A further possibility to determine the deterioration or deterioration condition of a battery lies in an active diagnosis. During this active diagnosis, the battery is charged or discharged with a predefined capacity. By measuring this active charge or discharge process, it is then possible to draw conclusions about the deterioration of the battery on the basis of the corresponding relationships that are known for the respective process. An active diagnosis method of this kind exemplified in European Patent Application EP 1 278 072 A1.